entropy

In Plato’s dialogue Cratylus, Socrates gives us one of Heraclitus’s most important ideas: You cannot step twice into the same stream. For Heraclitus, this idea epitomized his doctrine of flux — everything is constantly changing. Though it may seem as if you are stepping into the same stream a second time, so much has changed since you have stepped into it — you are feeling different water molecules, there are microscopic shifts in sediment, the temperature has changed by a thousandth of a degree, etc.